Arrests of people in traveling in family units have barely declined, despite extreme temperatures and the Trump administration’s “zero tolerance” policies at the border.

Overall illegal immigration has fallen this summer, but it is not clear if that is due to border enforcement policies or seasonal patterns.

Thousands of migrant families continued to pour across the southwest border in July despite dangerously hot summer weather and the Trump administration’s “zero tolerance” policy on illegal border crossing, according to government data released Wednesday.

A combined total of 12,285 people traveling in “family units” were either arrested or found to be inadmissible at ports of entry in July, according to Customs and Border Protection’s figures.

Of those, 9,258 were apprehended trying to sneak across the border illegally, between ports of entry. Such arrests are used as a proxy for illegal immigration with the idea that, assuming a given standard of border security, more apprehensions mean more illegal aliens are slipping undetected into the U.S. and vice versa.

While the number of family unit arrests for July ticked down by about 2 percent from June levels, it was still unusually high given the time of year and the Trump administration’s border enforcement policies. July was the fourth straight month that border agents arrested more than 9,000 people traveling in family units.

By comparison, just 3,389 people in family units were apprehended at the southwest border in July 2017.

The July arrest figures suggest family unit migration from Central America and Mexico is largely immune to historic patterns of illegal immigration, which tends to fall in the hot summer months. Family unit migration has remained stubbornly high even as triple-digit temperatures throughout the borderlands has caused more heat-related deaths of migrants this year than in 2017.

The Department of Homeland Security attributed the drop to tougher border enforcement under President Donald Trump.

“In the month of July, we saw a decrease in illegal border crossings because human traffickers and Transnational Criminal Organizations were put on notice that this Administration was increasing prosecutions of those entering the country illegally,” DHS spokesman Tyler Houlton said in a statement Wednesday. “Despite our terribly broken immigration laws, the administration has still been able to impact illegal immigration, but we need Congress to act to fix our system.”

The administration’s policies do not appear to have a mitigating effect on illegal family migration, however. Since April, when Attorney General Jeff Sessions announced a “zero tolerance” policy against illegal border crossing, family unit arrests at the southwest border have dropped by just 4 percent.

Sessions ruled in June that domestic and gang violence alone could not serve as the basis for a valid asylum claim, a move that is likely to foreclose petitions by thousands of asylum seekers from Central America and Mexico. The higher bar for claiming asylum has not yet made much of an impact — illegal immigration by family units was essentially the same the following month.

It remains to be seen if the stricter standard will deter illegal immigration by Central American families, most of whom cross the southwest border in order to petition for asylum.

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